Date of Award:

5-1976

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Department name when degree awarded

Range Science (Ecology)

Committee Chair(s)

Neil E. West

Committee

Neil E. West

Abstract

Studies of environmental and riparian vegetation interrelationships along the lower Escalante River were conducted during 1974 and 1975. The study area included the Escalante River flood terrace between Harris Wash and Coyote Gulch.

Methods were developed compatible for wilderness use. Sixty-nine 1 x 10 meter macro-plots were taken at 23 locations. Measurements were taken of major environmental parameters thought to influence riparian vegetation: stratigraphy, soil texture and moisture, river bank angle and aspect, and height and width of flood terraces.

Canyon profile was found to be strongly influenced by geologic strata. Resistance to erosion by these strata determines canyon fluctuations and flash floods further modify the river bank profile by creating three distinct flood terraces.

Vegetation distribution was found to be generally correlated with stratigraphy and flood terraces. The most dominant semi-aquatic species, Scirpus americanus and Eguisetum laevigatum were found on soils saturated to supersaturated with water on the low flood terraces. Baccharis emoryi was found in the medium and high flood terraces where the Chinle Formation was exposed. Different time periods between river inundations and flash floods created significantly different population age structures for the three major tree species (Salix exigua, Populus fremontii, and Tamarix pentandra). Tree longevity increased from low to high flood terraces.

Population age structure differences were attributed to flooding which dynamically maintains each cohort. Regeneration by root suckers for Salix and Populus have survival rates greater than Tamarix whose seedling source is washed away by periodic fluctuations in river level. Implications of this research are that reduction in river flow or regulation of floods would remove population equilibrium controls. Tamarix, without the effect of its seed source being washed away, would have a successional advantage over the other two native tree species whose densities in the young age classes are lower than that of Tamarix. Furthermore, tree populations would shift to an older age structure with greater density. Deleterious effects would be increased evapotranspiration and inaccessability to river recreation. The effects of such vegetation changes on wildlife are unknown.

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